SMAP, standing for Soil Moisture Active/Passive, is a NASA Environmental Research Satellite that combines a radar and radiometric instrument to measure land surface and soil moisture on a global scale at a very quick revisit rate to deliver data valuable in the understanding of Earth's water, energy and carbon cycles, as well as valuable information for the improvement of weather and climate forecasting, flood prediction and drought monitoring. Set for a three-year primary mission, the 944-Kilogram spacecraft will use a giant rotating reflector antenna to make its radar and radiometric measurements from a 685-Kilometer orbit. The SMAP mission and spacecraft are being developed and operated at the Jet Propulsion Laboratory with assistance from NASA's Goddard Spaceflight Center. Development of SMAP was initiated in 2007 as part of the Earth System Science Pathfinder Program after the National Research Council identified the mission as a high priority. NASA was able to put forward a heritage concept from the Hydros mission that was canceled for budgetary reasons in 2005. SMAP completed its concept review in 2008, allowing the in-depth development of spacecraft and instrument systems to begin.

By 2011, the instrument completed the Preliminary Design Review with the Critical Design Review of the entire spacecraft taking place in 2012, allowing hardware integration to begin ahead of a launch in 2015.

Image: NASA/JPL

The SMAP spacecraft was specifically developed as a one-off design with a platform based on the requirements of its payload to reduce the overall complexity of the spacecraft and ensure proper accommodation of the instrument from a structural point of view but also looking at the resources that are required such as electrical power, thermal control and data storage and downlink capability which was one of the more important drivers in the design of the platform. Also, the spacecraft was designed to maintain compatibility with a number of launch vehicles and payload envelope sizes, allowing the selection of the launch vehicle to take place late in the mission design process.

Photo: NASA Kennedy

SMAP is planned to operate from a sun-synchronous orbit at an altitude of 685 Kilometers at an inclination of 98 degrees – launched by a Delta II rocket. The local time of ascending node is 18:00. This orbit has an exact repeat cycle of 117 orbits (8 days), but due to the 1,000-Kilometer field of view of the instrument, SMAP achieves a repeat cycle of two days for high latitude locations (>45°) and three days for the equatorial regions. SMAP consists of a primary structure made of aluminum with a zenith deck that facilitates the Spun Instrument Assembly (SIA) and an anti-sun panel that builds the mounting surface for the radar system. The spacecraft bus itself is not spinning and consists of a pentagonal box structure that hosts external panels and an internal frame structure to provide mounting platforms for the various satellite systems.

External surfaces are used as radiators to dissipate excess heat into space. All structural components consist of aluminum and aluminum honeycomb materials. The subsystems are organized on the different external and internal panels so that they could be developed separately and integrated very easily. The SMAP spacecraft has a total mass of 944 Kilograms and in its deployed configuration it measures 9.7 by 7.1 by 6.8 meters while in its stowed configuration it is 4.8 by 1.7 by 1.9 meters in size. The bus itself measures 1.5 by 0.9 by 0.9 meters.

Photo: NASA Kennedy

Photo: NASA Kennedy

Photo: NASA/JPL

SMAP is equipped with a single solar array that is fixed in position and does not track the sun, requiring the spacecraft to point the array toward the sun for optimized power generation. The array is installed on one of the five larger side panels of the vehicle, consisting of one fixed and two fold-out panels connected to the central panel. The deployed solar array has a surface area of 7.8 square meters allowing the gallium-arsenide solar cells to generate a total power between 1,400 and 1,500 Watts. Dedicated regulators and control units are in charge of controlling the state of charge of the spacecraft batteries and distributing power to the various subsystems of the satellite using a 31-volt main power bus. SMAP is equipped with Lithium-ion batteries – a main battery with a 50 Amp-hour capacity and three auxiliary batteries with a total capacity of 28Amp-hours that reside within the launch vehicle adapter to deliver power during the ascent phase. Thermal control on the SMAP satellite uses a combination of passive and active systems. Multilayer insulation is used on the various satellite systems and survival heaters are installed on various components to ensure critical systems can maintain an operational temperature at all times. Heat from the electronics is rejected through external radiator panels. The battery pack is equipped with its own radiator, MLI and heater system since the efficiency of power storage strongly depends on the temperature the battery is kept at. SMAP employs an Attitude Determination and Control System that is based on previous heritage from a variety of missions, using a series of different sensors and actuators. Attitude determination is accomplished by a star tracker unit, sun sensors and inertial measurement units. The main sources of attitude information are the two star trackers of the spacecraft that are installed on a side panel of the vehicle, pointing to the zenith direction to be able to acquire images of the star-filled sky in a 10 by 10-degree field of view. Optical imagery acquired by the star tracker is analyzed by an algorithm that searches a catalog of thousands of bright star constellations to be able to precisely calculate the three-axis orientation in space.

Image: NASA/JPL

The Inertial Measurement System comes into play during re-acquisition of the spacecraft when attitude rates have to be reduced below the acquisition rate of the star trackers that can only track stars at low body rates. The system is also used to propagate attitude knowledge determined by the star trackers through gaps in stellar attitude updates. SMAP uses a redundant set of two Miniature Inertial Measurement Units manufactured by Honeywell. The Inertial Measurement Unit has extensive flight heritage and features a robust design using the GG1320 Ring Laser Gyro that provides precise rotation measurements.

The system uses the basic principle that counter-propagating laser beams have different frequencies with the difference dependent on rotation rate which can be measured to calculate the rotation rate about the RLG’s sensitive axis. The MIMU weighs 4.5 Kilograms being 23 by 17 centimeters in size. It has an operational measurement range of +/-375°/sec at a low bias of under 0.005°/hour. The system can tolerate the radiation conditions in Low Earth Orbit and handles accelerations of up to 25G. SMAP features 12 Sun Sensors installed on the various external panels of the spacecraft including the solar array. Data from all sensors is collected to calculate the direction of the solar vector with sufficient accuracy to keep the array pointed to the sun to ensure sufficient power generation in the event of a spacecraft safe mode. The Sun Sensors are also used for re-acquisition of the star trackers. Attitude actuation is provided by a Reaction Wheel Assembly and Magnetic Torque Rods. SMAP is equipped with three reaction wheels to provide three-axis pointing plus a fourth wheel that is used for momentum compensation to maintain a momentum balance between the spacecraft and Spun Instrument Assembly, counteracting any disturbance torques. The reaction wheel assembly is a rotating inertial mass that is driven by a brushless DC motor that spins the wheel. When accelerating the wheel, the satellite body to which the wheels are directly attached will rotate to the opposite direction as a result of the introduced counter torque.

Three Magnetic Torque Rods with redundant coils are used to create angular momentum by running a current through coils in the presence of Earth's magnetic field. The torquers are regulated by computers that control the current that is passing through the coils in order to control the force generated on each axis. The magnetic torquers are used during momentum dumps and for attitude control in spacecraft safe mode. Actuation of the torquers is commanded based on readings from a three-axis magnetometer.

Image: NASA

Orbit determination and position data is gained through two-way Doppler measurements performed several times a day. Position data is calculated onboard the spacecraft through propagation of Doppler measurements. GPS receivers were no option for the SMAP mission due to the blockage of a field of view to any GPS satellites caused by the large antenna atop the zenith panel of the satellite. SMAP uses a monopropellant propulsion system developed at JPL employing components with extensive heritage. A spherical titanium, diaphragm propellant tank manufactured by ATK holds 81 Kilograms of Hydrazine at launch, pressurized pre-launch and operated in blowdown mode throughout the mission. The propulsion system consists of eight 4.5-Newton thrusters that were also in use aboard the Cruise Stages of the MER and MSL Mars Rovers. The thrusters use redundant latch valves and pressure sensors to provide built-in redundancy.

To generate thrust, the system makes use of the catalytic decomposition of Hydrazine over a metallic catalyst bed. SMAP can use its propulsion system for orbit maintenance and corrections, attitude control and reaction wheel desaturations. The mission has a total delta-v budget of 112 m/s which is sufficient to maintain an operational orbit well beyond the design life of the spacecraft. The SMAP spacecraft uses an onboard Command and Data Handling Subsystem that builds on a number of previous JPL spacecraft to take advantage of lessons learned and minimize risk since SMAP uses a one-string architecture given the budget, mass requirements and planned duration of the mission.

The brain of the SMAP spacecraft is a RAD750 flight computer that has flown to space on several missions including Mars rovers and Earth observation satellites. RAD-750 is a single-card computer manufactured by BAE Systems in Manassas, Va. The processor can endure radiation doses that are a million times more extreme than what is considered fatal to humans. The RAD750 CPU itself can tolerate 200,000 to 1,000,000 rads. Also, RAD750 will not suffer more than one event requiring interventions from Earth over a 15-year period.

"The RAD750 card is designed to accommodate all those single event effects and survive them. The ultimate goal is one upset is allowed in 15 years. An upset means an intervention from Earth -- one 'blue screen of death' in 15 years. We typically have contracts that (specify) that," said Vic Scuderi BAE Business Manager.

RAD-750 was released in 2001 and made its first launch in 2005 aboard the Deep Impact Spacecraft. The CPU has 10.4 million transistors. The RAD750 processors operate at up to 200 megahertz, processing at 400 MIPS. The CPU has an L1 cache memory of 2 x 32KB (instruction + data) - to improve performance, multiple 1MB L2 cache modules can be implemented depending on mission requirements.

RAD750 operates at temperatures of -55°C to 125°C with a power consumption of 10 Watts. The standard RAD750 system can tolerate 100,000rads. SMAP uses the VxWorks operating system also found in many other missions including the Mars Exploration Rovers and the Mars Science Laboratory. Some elements of the operating software were developed specifically for SMAP, but teams were able to use a number of elements used in previous missions. The internal data system of SMAP uses PCI connections for the Command and Data Handling System while the backbone of the data system of platform and core is a 1553 data bus supporting the exchange of commands and housekeeping telemetry between the onboard computer and all subsystems including the attitude control system, power system and pyrotechnics control unit. An analog RS-422 bus is used for commanding of the radar and radiometer electronic control units. High-data rate communications between the instrument and the data systems are accomplished using a LVDS connection. Payload data is stored in a 128GB non-volatile memory.

Image: BAE Systems

RAD750 Card

SMAP employs a redundant S-Band communications terminal for command uplink and telemetry downlink via NASA's Earth Network and Space Network. The Tracking and Data Relay Satellite system can also be used for data exchange with the SMAP spacecraft if needed. Two redundant X-Band transmitters are used to deliver payload data to ground stations. The transmitters are facilitated on a fixed outrigger on the nadir (Earth-facing) panel of the spacecraft. S-Band communications reach data speeds of up to 512kbit/s while the high-speed X-Band link operates at 130Mbit/s.

The
S-band system includes a set of redundant 5-Watt transponders, a
single S-band low-gain antenna and a coaxial switch to select the
active transponder. The X-band telecomm system is comprised of
redundant 8-Watt transmitters, a single low-gain antenna and a
bandpass filter as well as switching electronics.
The SMAP spacecraft has been designed using a single-string
approach with redundancy in select systems such as the attitude
determination and control, propulsion, and communication systems.
Fault protection modes have been divided into two groups for
SMAP - the majority of faults will result in a spacecraft
standby mode in which the SIA is not de-spun. Only the most
severe faults will lead to a Primary Safe Mode or Emergency Safe
Mode requiring the SIA to be de-spun to place the spacecraft in
a safe state. Whenever SIA is de-spun, the attitude control
system has to cope with resulting torques and the re-initiation
of science operations at the end of a safe mode is a time-consuming
process that would lead to a gap in science data.

Image: NASA

SMAP Instrument

Image: NASA

The
356-Kilogram instrument of the SMAP spacecraft shares its name with the
spacecraft itself and, as the name states, consists of an active part, an
L-Band radar that sends radio pulses to the ground and records the echo, and a
passive part, an L-Band radiometer that just records the ambient microwave
emissions at the given wavelength range. Water, including water within the
soil, responds differently to microwave radiation than dry soil. The water
content influences the strength of the backscatter and the polarization of the
radiation. Backscatter from soil with a high water content is stronger and has
a different polarization than dry soil which can be detected by the instrument package.

As
with most microwave instruments, the antenna is the most prominent feature of
the instrument - in SMAP's case it is a 6-meter rotating mesh antenna that has
been one of the greatest challenges in the development of the spacecraft. The SMAP instrument consists of a rotating and a non-spun structure. The rotating part is comprised of an antenna boom, the deployable mesh antenna, the rotation mechanism and a series of front-end electronics.

The spinning instrument components reside on the zenith deck of the spacecraft to reduce overall spun mass/inertia, reduce radio frequency transmission line losses and lower the noise temperature for radiometer measurements.

The passive radiometer operates in a dual polarization mode covering linear horizontal and linear vertical polarized signals while the radar instrument can operate in HH (pulse-receive), VV and HV polarization. One of the major objectives of SMAP was a rapid revisit time in the range of two to three days, requiring a wide ground swath of 1,000 Kilometers to be covered by the instrument. Furthermore, the chosen L-Band frequency and desired spatial resolution dictated the size of the antenna aperture. Radiometer and radar share the same antenna and feed horn accomplishing the simultaneous radar and radiometer requirements - implementing diplexers to separate the active from the passive bands that use different frequency ranges. All of the radiometer electronics reside on the spun side of the rotating Reflector Boom Assembly (RBA) while the radar electronics are hosted on the satellite platform because of thermal requirements.

The spun-side of the SMAP instrument features the single feedhorn, the diplexers, the Deployment and Spin Motor Control Unit, and the Radiometer Electronics. The Spun Platform Assembly includes the primary and secondary structures. The former provides the backbone of the instrument, being the installation platform for the antenna boom while the secondary structure facilitates the shared feedhorn of the instrument and the Integrated Feed Assembly electronics box.

SMAP employs a conical-scanning geometry with a spinning antenna reflector rotating 14.6 times per minute around the nadir-pointing axis of the spacecraft. The rotation frequency was chosen to achieve the desired field of view with minimal overlap in between sans in the along-track direction. The RBA has a mass of 65 Kilograms including its launch restraint that holds the boom in a fixed position with the stowed antenna held to the spacecraft side. The spinning portion of RBA weighs 49 Kilograms.

The core of the spin subsystem is a Bearing and Power Transfer Assembly that includes the spin motor with associated bearings, an RF rotary joint of the radar, and 65 slip rings forming the electrical and data connection between the spun and not-spun side of the SMAP instrument. In addition to the physical power and data interfaces through the slip rings, both sides of the interface also include radio equipment for data transfer.

Image: NASA

Image: NASA/JPL

Instrument Block Diagram

The physical interfaces are power supplies to the Radiometer Electronics and the Deployment and Spin Motor Controllers, and data interfaces with the instrument electronics and spacecraft Command & Data Handling Systems. Radio interfaces are used between the Radiometer and Radar electronics and the instrument electronics unit that reside on the non-spun side.

Image: NASA Kennedy

Image: NASA/JPL

Image: NASA/JPL

The
Bearing and Power Transfer Assembly resides within the cylindrical
section of the instrument that also serves as mounting structure for all
spun-side equipment. All spun-side motors, thermal control equipment,
command and telemetry systems are controlled from the Integrated
Control Electronics. The Front End Electronics, passive RF components,
the feed horn are installed on separate structures from the Spin
Control Electronics to optimize the spun mass properties. A Cone Clutch
Assembly builds the interface between the spun platform assembly and
the spacecraft bus.

All
the spinning elements are referred to as Spun Instrument Assembly
SIA. The Spun Instrument Assembly is balanced by offsetting the feed
and spin electronics assemblies from the spin axis and adding small
balance masses in key locations.

The
Reflector Boom Assembly consists of a Boom Deploy Spooler and
Actuator, a lower boom segment, an elbow hinge, an upper boom segment, a
boom restraint and the Reflector itself with its own Deploy Spooler
& Actuator. The 5-meter long boom itself consists of two
graphite-epoxy tubes to form a lightweight and stable system.
Deployment of the boom is completed in a 16-minute sequence as launch
locks are opened by pyrotechnics and spoolers and actuators wind a
cable that pulls the two-hinged boom to its fully extended position.

Boom deployment is followed four days later by the 33-minute deployment
of the antenna reflector using its own spooler and actuator. During
the deployment, the spacecraft attitude control system is placed in
idle mode.

The
reflector used by SMAP was provided by Northrop Grumman marking the
first time the deployable Astromesh reflector is used in a scientific
instrument deployed into a Low Earth Orbit, and the first time it is
used with a microwave radar and radiometer instrument. Normally, the Astromesh reflector is
used on communications satellite acting as antenna reflector.

The reflector consists of a perimeter tube featuring composite tubes that support front and rear webs of fiber-reinforced tape. The reflective surface consists of a gold-plated molybdenum wire mesh that is secured by a net connected to a front web to ensure the reflective surface remains in a parabolic shape. Interfacing with the boom is a prime batten that is mated to the perimeter truss segment which can fould out like a camping chair to enter a relatively stable configuration while being of a low-mass design.

The mesh uses a 20 OPI Structure (Openings per inch) that was chosen based on a compromise between mass and emissivity, meeting the L-Band emissivity requirements. For proper soil moisture measurements, the antenna reflector went through a calibration campaign to allow temperature estimations once in orbit in order to perform antenna pattern correction during data processing.

Image: NASA/Northrop Grumman

Image: NASA

Using an Offset-fed deployable parabolic reflector design, the SMAP instrument achieves a focal length of 4.2 meters operating at a beamwidth of 2.7° for the radar and 2.5° for the radiometer. The antenna is pointed 35.5 degrees off the spin axis creating a 40-degree incidence angle. Due to the large size of the instrument field of view, the cone swept out by the antenna is slightly obstructed by the upper corners of the two outer solar panels. Analysis showed that the resulting performance perturbations are negligible.

Because of the antenna design, tests of actual flight hardware on the ground were not possible with the exception of tests of exact scale models and software-based analysis to determine relevant parameters such as gain, half-power beamwidth, sidelobe and cross-polarization levels, and electrical pointing.

Spin-up of the antenna is accomplished in two stages due to limitations imposed by the attitude control system that will have to counter the torque introduced into the spacecraft bus which would start rotating into the opposite direction from SIA. Momentum will be compensated by the reaction wheels as SIA spins up to 5 RPM. After desaturating the wheels, SIA can continue the spin-up to reach the proper 13 to 14.6 RPM rotation speed.

Image: NASA

Image: NASA

The
30-Kilogram radiometer measures microwave emissions for horizontal
and vertical polarization in order to determine brightness temperatures. It includes digital
electronics and spectral filtering for radio frequency interference
mitigation. It is approximately 0.9 by 0.8 meters in size.
Radiometers are required to make repeatable measurements with
monotonic responses over the operational temperature range & over the
course of an extended period of time. SMAP’s radiometer is equipped
with a titanium thermal isolator and Expanded Polystyrene radome for
short-term temperature stability and an active thermal control
system with set-point adjustment to be able to control the
temperature of the instrument over the long term. With an active
system, the instrument temperature can be changed in orbit which
will allow for the correction of gain non-linearities.

The
single feedhorn of the SMAP instrument is shared between the radar
and radiometer instruments, interfacing with a diplexer that
separates the passive and active bands through high RF frequency
isolation and pre-select filtering for interference rejection. The
diplexer assembly also includes the high-power electronics for the
radar.

The L-Band Radiometer
operates at a frequency range of 1,400 to 1,427 MHz delivering data
in vertical and horizontal polarization and the 3rd & 4th Stokes Parameters.
The system operates at a thermal accuracy of 1.3K and a ground
resolution of 10 Kilometers, using a sample frequency of 3.2kHz.

Image: NASA

Zenith-mounted SMAP Instrument Components

The nominal data rate for the radiometer is 4.3Mbit/s. Calibration of the radiometer is accomplished by making regular observation of stable Earth and space targets as well as internal calibration targets. Horizontal and vertical linear polarizations are selected through an Orthomode Transducer. Front end electronics used by the Radiometer include a calibrated noise source. The front and back end electronics form a heterodyne radiometer that completes a downconversion of predetected horizontal and vertical polarization component signals to a 120MHz intermediate frequency.

The two polarization channels are then digitized and processed by the Radiometer Digital Electronics at 96MHz with a 14bit resolution. The Radiometer uses a fully digital back-end processor that is in charge of Radiometer Digital Signal Processing and interference mitigation. The Radiometer Digital Electronics represent the first spaceborne back-end processor subsystem. It utilizes FPGA-based digital signal processing which uses time, frequency, statistical and polarization diversity to detect and tag interference events.

The Radiometer Digital Electronics consist of Circuit Card Assemblies, a connector panel and structural components. The Circuit Card Assemblies are comprised of two Analog Processing Units covering the vertical and horizontal channels, performing quadrature down-conversion, subbanding and sub-channel generation. The Data Processing Unit is in charge of controlling all radiometer functions, processing, timing and packetization of data from the radiometer and the digitization of telemetry from all radiometer components. A Power Distribution Unit converts the primary power from the SMAP spacecraft at 28 Volts and generates the different secondary voltages for powering all Radiometer subsystems.

Image: NASA

Radiometer Block Diagram

The 49-Kilogram, 1.5 by 0.9-meter L-Band radar delivers radar impulses from a 500-Watt transmitter (peak) that operates at a 2,850 Hz pulse repetition frequency. It operates in a frequency range of 1,217 to 1,298 MHz making measurements in Vertical-Vertical polarization (transmit-receive), H-H and H-V polarization. The radar is operating at an accuracy of 1.0dB. It achieves a ground resolution of 250 by 400 meters and delivers raw data at a rate of 35Mbit/s. The radar employs pulse compression in range and doppler discrimination in azimuth to achieve a sub-division of the antenna footprint in order to reach the desired spatial resolution that surpasses that of the Radiometer.

Image: NASA

Radar Functional Diagram

Image: NASA

Radar Pulse Sequence

Operating at the normal pulse repetition frequency, the radar transmits two 15-mcirosecond pulses one in vertical and one in horizontal polarization followed by a 42-microsecond dwell time during which the radar echo is recorded and the radiometer completes a single integration with active and passive signals being separated by the diplexer unit.

The SMAP radar is capable of completing initial data processing on board in order to generate the sub-footprint resolution that is necessary for geophysical retrievals. The onboard processor can process raw data into low and high-resolution data that is downlinked to the ground for further processing to deliver low and high-resolution radar products.

One major concern for data accuracy on SMAP is Radio Frequency Interference since the L-Band range is used by many ground-based systems which can pose a major problem when aiming to obtain clean readings without any foreign L-Band emissions.

For the radiometer, a number of techniques are utilized to identify and correct for pulsed and narrow-band sources that may interfere with the instrument. Pulsed sources can be detected through simple time-domain pulse threshold strategies since the sampling rate of the radiometer is very high, allowing sub-millisecond interference detection. Continuous wave detection is more difficult and requires the radiometer’s 24MHz bandwidth to be filtered into sixteen 1.5MHz sub-bands with detected power levels being recorded for each band so that a 1.5 MHz x 1ms spectrogram can be generated to go through different interference detection methods in ground-based data processing.

In contrast to the radiometer, the radar actually operates in a shared band that is also used by civil/military navigation & air traffic comms, so significant interference can be expected. The interference occurs mostly in narrow-bands, but since SMAP’s radar also operates at a 1MHz narrow band chirp a key interference avoidance technique for the radar will be to adjust the center of the transmit frequency. If a persistence source of interference is detected in a given band or over a particular location, the center frequency is commanded to another location in its operational spectrum. Interference detection and removal will be performed as part of ground-based data processing.

Overall, the SMAP instrument will achieve a measurement accuracy of 0.04 cubic meters of water per cubic meter of soil in the top 2-5 centimeters for vegetation water content. Soil Maps will be spaced at 10 Kilometers while freeze/thaw maps can distinguish areas as small as 3 Kilometers.

SMAP Data Paths

Image: NASA

Ground Segment

The SMAP ground segment includes components in charge of planning and sequencing spacecraft activities, components that support real time operations and components that enable science data processing and exchange. A high degree of automation is used for real time operations to save overall mission cost. SMAP uses NASA’s Advanced Multi-Mission Operations System to provide telemetry processing, storage, reporting and a subset of automation capabilities for real-time operations.

SMAP uses the Near Earth Network to deliver telemetry and instrument data to the ground and receive command sequences several times per day. NEN ground stations used by SMAP include the McMurdo Station in Antarctica with ten contacts per day for at total of 91 minutes, Svalbard Station in Norway with ten contacts per day for 88 minutes, Fairbanks in Alaska with 7 contacts for 54 minutes and Wallops, Virginia with three contacts for 26 minutes. The Tracking and Data Relay Satellite System can be used for housekeeping data downlink and command uplink to the spacecraft in case short-term commanding is needed. Telemetry and housekeeping data is handled in S-Band only while the NEN ground stations support the X-Band downlink at data rates up to 130 Mbit/s. Scheduling and pass reporting are managed by the Data Services Management Center, White Sands.

The SMAP mission operations center at JPL is responsible for spacecraft instrument and bus health monitoring, science and housekeeping operations planning and instrument data storage. Science data downlinked from SMAP is relayed to the Data and Operations System Level Zero Processing Facility at the Goddard Spaceflight Center where raw data is formatted into files and radar & radiometer data is supplied to the Science Data System for further processing. This data is then used by the Mission Operations Center to be combined with housekeeping information such as timing, pointing, and ephemeris information.

Data retrieval algorithms for SMAP were developed pre-launch and verified through a series of field campaigns that validated the principles of soil moisture retrievals through SMAP data. These observations were made using airborone sensors covering soils with different water content at different times of year in Canada, the United States and Australia. Further in-situ measurement campaigns will be conducted in coordination with SMAP passes in order to provide calibration data in the early phase of the mission.

A special SMAP Applications Program has been initiated to allow for a better interaction between data application users and mission scientists to better reach users and use their feedback in order to improve data distribution, formatting and other items that allow for a more rapid ingestion of soil moisture data into decision-making environments by the various user groups. The Applications Program has already gained an international membership covering areas such as agricultural productivity, drought & wildfire risk assessment, floods and landslide prediction, human health and national security.

SMAP Data Products

Image: NASA

SMAP Science

The overall
objective of SMAP is to monitor and map global soil moisture at an
unprecedented resolution, sensitivity, spatial coverage and revisit times. Data
delivered by SMAP will be used in the examination of the relationship between
soil moisture, soil freeze/thaw state, and associated environmental properties
in a global scale to put processes into a perspective within the overall
land-atmosphere carbon, water and energy exchange and vegetative activity.

Monitoring soil moisture allows insight into evaporation and transpiration
rates and processes at the land-atmosphere boundary. Following the global water
is important because of the relatively large energy needed to vaporize water,
giving it a significant role within the Earth's energy cycle. Water has a large
influence on weather and climate on large and small scales over continental
regions. Obtaining correct soil moisture data can enhance weather prediction
models, and seasonal climate models.Gaining a
continuous insight into soil moisture variations will allow a better prediction
of weather and climate over continental regions with extended lead times and
positive effects on socioeconomic activities such as water management,
agriculture, flood prediction, drought monitoring and identification of other
potential hazards associated with water in the soil. Model predictions of water
availability for agriculture and other activities are currently the only way of
moisture monitoring. SMAP will deliver data to allow a significant improvement
of these models through the collection of space-based soil moisture
observations. Flood
forecasts can be improved through the use of high-resolution moisture profiles
and freeze/thaw status of areas helping in the identification of possible flood
and landslide hazards. SMAP data
will be useful in applied agriculture since water availability and
environmental stress are important factors in the estimation of plant
productivity and potential yield. Additionally, frost damage can be limited by
employing freeze/thaw maps. Another aspect of soil moisture measurements and
freeze/thaw status is the application in the prediction of the expansion of
many diseases that are constrained by the timing of frozen temperatures and/or
water availability. Heat stress and virus spreading rates can also be modeled
through the use of this type of data.Operational
application of soil moisture data will be realized in the assessment of ground
trafficability for remote operations or military activities. Forecasting of
low-level fog, aviation density altitude and dust generation is possible
through SMAP data. Furthermore, radar scans over large bodies of water provide
information in ice cover, relevant to ship traffic across the globe.

Image: NASA

Image: NASA

Image: NASA

SMAP Mission Objectives (per NASA)

Understand processes that link Earth’s water, energy and carbon cycles on land. Soil moisture links the water and energy cycles through evaporation, as described in the preceding section, and links the water and carbon cycles through the plant processes of photosynthesis and transpiration. Better measurements of soil moisture are likely to increase scientists’ understanding of how these basic Earth system cycles link together.

Estimate flows of water and energy between the atmosphere and land globally. SMAP’s highresolution measurements will improve the accuracy of estimates of these important exchanges.

Quantify the net transfer of carbon between the boreal forests and atmosphere. The overall role of northern forests in the carbon cycle, and their future role, remain unanswered questions. SMAP’s measurements will provide new data on how carbon enters, leaves and is stored in these data-sparse landscapes.

Enhance weather and climate forecasting accuracy. The patterns of soil moisture affect heating at Earth’s surface and the development of severe weather. With realistic soil moisture inputs into weather prediction models, the forecasts will improve where most needed: over land.

Develop improved flood prediction and drought-monitoring capability. Knowing soil moisture will allow hydrologists to make better decisions related to the risk of flooding or drought, such as how much water to retain in reservoirs.

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